Device and process for liquid treatment of wafer-shaped articles

ABSTRACT

A device for liquid treatment of a defined area of a wafer-shaped article, especially of a wafer, near the edge, in which the liquid is applied to a first surface, flows essentially radially to the outside to the peripheral-side edge of the wafer-shaped article and around this edge onto the second surface, the liquid wetting a defined section near the edge on the second surface and thereupon being removed from the wafer-shaped article.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.10/164,424 filed on Jun. 10, 2002. Application Ser. No. 10/164,424 is aDivisional of U.S. patent application Ser. No. 09/556,426 filed on Apr.24, 2000, now U.S. Pat. No. 6,435,200. The entire contents of theabove-identified applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a device and a process for liquid treatment ofa defined section of wafer-shaped article, a section near the edge,especially of a wafer.

The reason for treatment of a defined section of wafer-shaped articlenear the edge, especially of a wafer, will be described below.

A wafer, for example a silicon wafer, can for example have a silicondioxide coating on all sides. For subsequent processes (if for example alayer of gold or a layer of polysilicon (polycrystalline silicon) is tobe applied), it can be necessary to remove the existing coating from thewafer at least in the edge area of the main surface, but optionally alsoin the area of its peripheral surface and/or the second main surface.This is done by etching processes which can be divided mainly into dryetching processes and wet etching processes.

Another application is the cleaning of wafers. Here it can be necessaryto clean a wafer at least in the edge area of a main surface, butoptionally also in the area of its peripheral surface and/or the secondmain surface, i.e. to remove particles and/or other contamination. Thisis done by wet cleaning processes.

The invention is aimed at wet etching and wet cleaning (combined underthe concept of liquid treatment). In doing so the surface area of thewafer to be treated is wetted with the treatment liquid and the layerwhich is to be removed or the impurities are carried off.

A device for executing this liquid treatment is described for example inU.S. Pat. No. 4,903,717. In this device the wafer-shaped article (wafer)is mounted on a spin chuck. The treatment liquid, for example, anetching liquid, is applied to the wafer surface to be treated, theliquid is distributed as a result of the rotational motion of the waferover its surface and is flung off laterally over the edge of the wafer.

To prevent the treatment liquid from reaching the surface which is notbe to treated in an uncontrolled manner, in U.S. Pat. No. 4,903,717 achuck is proposed which flushes the surface which faces the chuck andwhich is not to be treated with a gas. In doing so the gas emergesbetween the wafer edge and the chuck.

JP 09-181026 A describes a chuck for semiconductor wafers which outsideof an annular nozzle has a special shape, for example an annular stepwhich falls away to the outside or a bevelling of its edge. In addition,a suction opening is proposed. This shaping of the intake opening isdesigned to influence (reduce) the flow velocity in the edge area. Thisis intended to serve such that the treatment liquid which has beenapplied from overhead flows beyond the edge of the wafer onto the sidefacing the chuck and treats the edge area there.

Regardless of whether a means to hold the wafer-shaped article (chuck)is used as claimed in U.S. Pat. No. 4,903,717 or JP 09-181026 A, an edgearea of 1.5 mm (measured from the outer edge of the wafer) at most canbe treated on the main surface facing the chuck. The liquid afterwardsflows back in the direction of the wafer edge and is flung off by it.

SUMMARY OF THE INVENTION

Accordingly the object of the invention is to demonstrate onepossibility for treating a defined, edge-side area with a liquid on onesurface of a wafer-shaped article and it is also to be possible to treatan edge area of more than 2 mm (measured from the outside edge of thewafer).

Accordingly, the invention in its general embodiment proposes a devicefor liquid treatment of a defined section of a wafer-shaped article,especially a wafer, near the edge, with a means for holding thewafer-shaped article, with a gas feed means for at least partial gasflushing of the surface of the wafer-shaped article which faces themeans, in which on the peripheral side there is a gas guide device whichroutes most of the flushing gas in the edge area of the wafer-shapedarticle away from the latter.

The holding means (chuck) is used to hold the wafer for this purpose.Here holding can be done using a vacuum or the wafer floats on an aircushion and is prevented from sliding off sideways by lateral guideelements.

The wafer can also be held by the gas which flows past on the bottom ofthe wafer forming a negative pressure (also called the Bernoulli effect)by which the wafer experiences a force in the direction of the chuck.The wafer is touched by an elevated part of the chuck within the gasfeed device, by which the wafer is prevented from sliding off sideways.

Via the gas feed line the gas can be routed onto the bottom (the surfacewhich faces the chuck) of the wafer-shaped article (wafer) in order toprevent the liquid from reaching this bottom and thus executing unwantedtreatment.

The gas used for this purpose should be inert to the surface onto whichit is flowing; for example, nitrogen or extremely pure air are suited.

The gas feed means can consist of one or more nozzles or an annularnozzle. These nozzles should be attached symmetrically to the center ofthe chuck in order to enable uniform gas flow over the entire periphery.

The gas guide device is used to route the gas which flows from themiddle part of the chuck in the direction of the edge of the wafer awayfrom the edge area. The gas now flows past the side of the gas guidedevice which faces away from the wafer-shaped article. The fartherinside (towards the center of the chuck) this gas guide device isattached, the larger the edge area is at this point.

Since in the section of the bottom of the wafer near the edgeessentially gas can no longer flow to the outside, in treatment with theliquid the latter can flow around the wafer edge onto the bottom andthus can wet the section of the wafer bottom near the edge.

The advantage of the invention over the prior art is that the size ofthe section near the edge can be any size desired by means of suitableselection of the gas guide device.

The gas stream which flows past the gap between the gas guide device andthe wafer can produce a negative pressure within the gap by suitableshaping of the gas guide, by which in addition in the edge area the gasflows from the vicinity of the wafer edge to the inside. During liquidtreatment the liquid is thus sucked into the edge area.

In one embodiment the gas guide device has the shape of a ring. Thisring can be attached to the base body of the chuck using for examplethree or more spacers. But it can also be machined out of the base bodyby corresponding milling.

The ring in one embodiment has an inside diameter which is smaller thanthe outside diameter of the wafer-shaped article and an outside diameterwhich is at least the same size as the outside diameter of thewafer-shaped article.

In this way the liquid which flows around the peripheral-side edge ofthe wafer-shaped article (around the wafer edge) can be captured by thering and delivered to the inside.

The gas guide device can also be formed by an annular groove which isconcentric to the periphery of the means and from which the gas isdischarged to the outside. This can be ensured by simple holes whichlead to the outside from the bottom of the groove in the base body ofthe chuck.

In another embodiment the gas guide device on its inner periphery has asharp edge (edge angle less than 60°). In this way almost all the gascan be routed away in the edge area from the wafer.

In one embodiment the part of the means which is located between the gasfeed means and the gas guide device (base body) is located at a greaterdistance to the wafer-shaped article (wafer) than the gas guide deviceto the wafer-shaped article. In this way more gas can flow between thewafer and this part (base body) than between the wafer and the gas guidedevice. Most of the gas on the side of the gas guide device facing awayfrom the wafer must therefore flow past this device.

Advantageously the gas guide device is configured such that if there isa wafer-shaped article (wafer) on the chuck the gas guide device doesnot touch the wafer-shaped article (wafer), i.e. a gap remains betweenthe wafer and the ring.

This gap between the gas guide device and the wafer-shaped article inone embodiment is 0.05 to 1 mm, advantageously 0.1 to 0.5 mm. In thisway, between the wafer and the gas guide device a type of capillaryforms, from which the liquid which has flowed around the wafer edge issucked. The inside diameter of the surface which faces the gas guidedevice and which is wetted by the liquid is smaller than the insidediameter of the annular surface of the gas guide device.

It is advantageous if the surface of the gas guide device facing thewafer-shaped article is parallel to the main surfaces of thewafer-shaped article. The gap between the wafer-shaped article (wafer)and the gas guide device is thus the same size in the entire edge area.

One embodiment calls for the chuck being able to be caused to rotate.This is advantageous, even if not necessary, since the treatment liquidcan be flung off both from the chuck and also the wafer edge. If thechuck is not in rotation during liquid treatment, the liquid isentrained or blown off by the gas flow.

Another part of the invention is a process for liquid treatment of adefined area of a wafer-shaped article, especially of a wafer, near theedge. In this process the liquid is applied to a first surface facingthe liquid source. The liquid flows essentially radially to the outsideto the peripheral-side edge of the wafer-shaped article (wafer edge) andaround this edge onto the second surface which faces away from theliquid source. The liquid wets a defined section near the edge on thesecond surface and is thereupon removed from the wafer-shaped article.

The advantage over the prior art is that in this process the part of theliquid flow which reaches the section of the second surface near theedge also flows on the second surface in a stipulated direction(originating from the edge (wafer edge) in the direction of the wafermiddle) and need not flow back again to the edge. Rather the liquid isremoved from the inside edge of the section near the edge. This can takeplace for example with a device as claimed in the invention.

In one embodiment of the process the edge area is chosen to be largerthan 2 mm.

In another embodiment of the process the wafer-shaped article duringliquid treatment rotates around its axis, by which the treatment liquidis flung off the edge of the wafer-shaped article or the-wafer edge.

Advantageously the rotational velocity is at least 100/min in order toeffectively fling off the-liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

Other details, features and advantages of the invention follow from thedescription below for the embodiments of the invention which are shownin the drawings.

FIG. 1 schematically shows an axial section of the means (chuck 1)including a wafer which is located on it.

FIGS. 2 and 3 schematically show an axial section of the edge area ofthe chuck. Gas routing is apparent in it. Moreover FIG. 3 shows themotion of the liquid during treatment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The chuck 1 consists essentially of three parts (2, 3, 4), the base body3, the cover 2 and the gas guide device 4. The base body 3 is madeannular and is joined to a hollow shaft (not shown) which on the onehand can cause the chuck to rotate (shown by the arrow R) and on theother hand can supply the gas feed means (5, 6) with gas G.

The cover 2 is inserted into the base body and is joined to it (notshown) such that between the cover 2 and the base body 3 an annular gaschannel 5 is formed which on the top (the side facing the wafer)discharges into an annular gap, the annular nozzle 6. The diameter ofthe annular nozzle 6 is smaller than the inside diameter of the gasguide device 4.

This chuck works according to the “Bernoulli principle”. Outside theannular nozzle 6 (in area 7) a gas cushion is formed on which the waferfloats. The wafer is prevented from sliding off sideways by guideelements which are attached on the peripheral side (pins 25) and thewafer is entrained by them when the chuck rotates around the axis A. Thepins can be moved to rest against the edge of the wafer (compare U.S.Pat. No. 4,903,717).

The gas guide device 4 has the shape of a ring and is attached on thebase body 3 on the top (the side facing the wafer) using a plurality ofspacers 21 which are distributed regularly on the periphery. The ring 4has an inside diameter which is smaller than the outside diameter of thewafer W and an outside diameter which is larger than the outsidediameter of the wafer W.

The surface 14 of the gas guide device facing the wafer W is a flatannular surface which is parallel to the main surfaces of the wafer.Between the surface 14 and the surface of the wafer facing the chuck,when the wafer is located on the chuck, an annular gap 10 is formed. Thedepth of the gap c (FIG. 3) corresponds to the difference of the outsideradius of the wafer W and the inside radius of the gas guide device 4.The width a (FIG. 2) is formed by the distance from the surface 14 tothe wafer surface facing the chuck.

Between the gas guide device 4 and the base body 3 an annular gasdischarge channel 8 is formed into which the gas is discharged by thegas guide device 4. The total cross section of the gap 10 is muchsmaller than that of the gas discharge channel 8, by which the channelcan discharge most of the gas.

In the area 7 between the wafer W and the base body 3 or between theannular nozzle 6 and the gas guide device 4 the gas flows directly alongthe wafer surface facing the chuck. The narrowest cross section in thisarea is located between the surface 13 (the surface of the base body 3facing the wafer) and the wafer and is shown in FIG. 2 by b. Thedistance b of the base body 3 to the wafer is larger than the distance aof the gas guide device to the wafer. The surface 12 of the cover 3facing the wafer is located essentially in the same plane as the surface13 of the base body.

If the wafer is located on the chuck, it is held suspended by the gascushion in area 7, its touching neither the cover 2 nor the gas guidedevice 4. The gas escapes from the annular nozzle 6 (gas flow G1) and isdischarged via the gas discharge channel 8 (gas flow G2). A small amountof gas can escape via the gap 10, but a negative pressure is probablyproduced by the gas flow G2, by which even gas from the vicinity isintaken via the gap 10 and is entrained by the gas flow G2.

During liquid treatment the liquid is applied to the surface facing thechuck 1, the liquid then flows in the direction of the wafer edge(liquid flow F) and around the wafer edge E. When the wafer rotates someof the liquid can be flung off directly from the wafer edge (not shown).Then the liquid flow is divided into two flows F1 and F2. The liquidflow F1 flows away from the wafer.

The liquid flow F2 flows into the gap 10 and thus wets the bottom of thewafer. F2 wets the edge area of this surface somewhat farther than thegas guide device extends to the inside. Therefore the wetted area d issomewhat larger than the depth of the gap c. Here the liquid flow F2 isdeflected by the gas flow G2 around the inner edge of the gas guidedevice and the liquid flow F2 and the gas flow G2 leave the chuckjointly via the gas discharge channel.

1. A device for wet etching with a liquid a defined area of a firstsurface of a wafer-shaped article, the defined area being adjacent to aperipheral edge of the wafer-shaped article, the device comprising:holding means for holding the wafer-shaped article with the firstsurface facing, within the defined area, a surface of said holding meansthat is parallel to the first surface, said holding means comprising gasfeed means for at least partial flushing of a gas from the firstsurface, and a gas guide in a periphery of said holding means; and saidgas guide being arranged to be separated from the first surface by a gapand having a channel to divert most of the gas away from the definedarea when the wafer-shaped article is being held by said holding means,said gap having a width that permits creation of a capillary force thatcauses the liquid to enter into said gap and to wet and etch the definedarea of the first surface adjacent to the peripheral edge, whereinwithin the defined area, a surface of said gas guide facing the firstsurface is parallel to the first surface.
 2. The device of claim 1,wherein said gas guide is ring-shaped.
 3. The device of claim 2, whereinsaid ring-shaped gas guide has an inner diameter that is smaller than anoutside diameter of the wafer-shaped article and an outside diameterthat is at least a same size as the outside diameter of the wafer-shapedarticle.
 4. The device of claim 1, wherein said gas guide is formed byan annular groove that is concentric to said periphery of said holdingmeans and from which a gas is discharged.
 5. The device of claim 1,wherein a part of said holding means is located between said gas feedmeans and said gas guide, and said part is located at a greater distancefrom the wafer-shaped article than said gas guide is from thewafer-shaped article.
 6. The device of claim 1, wherein said gap is 0.05to 1 mm.
 7. The device of claim 1, wherein said gas guide is annular andsurrounds said holding means and said gas feed means.
 8. The device ofclaim 1, wherein said gas guide comprises a radially inward projectionthat diverts the gas away from the defined area.
 9. A device fortreating with a liquid a wafer-shaped article having a first surface, asecond surface opposite the first surface, and a peripheral edge betweenthe first and second surfaces, the device comprising: holding means forholding the wafer-shaped article with the second surface facing saidholding means, said holding means comprising gas feed means for at leastpartial flushing of a gas from the second surface, and a gas guide in aperiphery of said holding means; said gas guide being arranged to beseparated from the second surface by a gap when the wafer-shaped articleis being held by said holding means, said gap having a width thatpermits creation of a capillary force that causes the liquid to enterinto said gap and to wet and treat a defined area of the second surfaceadjacent to the peripheral edge, wherein within the defined area, asurface of said gas guide facing the second surface is parallel to thesecond surface; and a channel that branches from a radially inward endof said gap.
 10. A device for treating with a liquid a wafer-shapedarticle having a first surface, a second surface opposite the firstsurface, and a peripheral edge between the first and second surfaces,the device comprising: holding means for holding the wafer-shapedarticle with the second surface facing said holding means, said holdingmeans comprising gas feed means for at least partial flushing of a gasfrom the second surface, and a gas guide in a periphery of said holdingmeans; said gas guide being arranged to be separated from the secondsurface by a gap when the wafer-shaped article is being held by saidholding means, said gap having a width that permits creation of acapillary force that causes the liquid to enter into said gap and to wetand treat a defined area of the second surface adjacent to theperipheral edge, wherein within the defined area, a surface of said gasguide facing the second surface is parallel to the second surface; andsaid gap extending radially inward from the peripheral edge to a recessin the holder, the radially inward extent of the gap defining thedefined area.